Combine the wine and sugar in a small saucepan and place over medium heat.
Bring to a simmer and cook, gently swirling the pan every now and then, until the sugar has completely dissolved and the wine has reduced by about half.
You want it to be thickened and syrupy (it will continue to thicken as it cools).
Remove from the heat and allow to cool to at least room temperature (chilled is even better for the shakes).
For the Milkshakes:
To a blender, add the red wine syrup (I save a couple tablespoons for garnishing the finished milkshakes), milk, hot fudge/chocolate syrup, ice cream, and vanilla.
Puree until well blended, thick, and creamy. Add more milk or a handful of ice to achieve your desired consistency.
Divide the mixture between two tall glasses and garnish as desired. I like to do another drizzle each of the hot fudge (I even pour some in the empty glasses first) and wine syrup, whipped cream, flaky sea salt, and fresh berries.